With the development of the information society, people have a growing demand on the display devices; in order to satisfy the requirements, a plurality of flat panel display devices such as an LCD, a Plasma Display Panel (PDP) and an Organic Light Emitting Diode (OLED) have been rapidly developed recently. In the flat panel display devices, the LCD has basically replaced the cold-cathode display device due to the advantages of light weight, small size and low energy consumption.
However, the Thin Film Transistor LCD (TFT-LCD) itself is beginning to receive new challenges of the display technology, for example, the TFT-LCD itself has some inherent disadvantages; with the development of technology, the disadvantages are increasingly challenged, and are increasingly unable to be accepted by the consumers and technology trends. Relative to the OLED, the TFT-LCD mainly ahs the following problems:
1) passive lighting, so, no matter it is a black screen or a white screen, the backlight needs to be turned on all the time, which causes high energy consumption; in the TFT-LCD, the liquid crystal is only used as a light valve to control the penetration and blockage of the light, and the liquid crystal itself cannot light, thus, the backlight must be turned on no matter it is a black screen or a white screen; although a Local Dimming technology is put forwarded in the TFT-LCD, the algorithm is complicated, and is unable to adapt to most of the display pictures, some Local Dimming which is unequally displayed is easy to occur; and even if used, the backlight cannot be truly turned off, and a certain energy consumption also exists.
2) lower aperture ratio, which further reduces the utilization rate of energy; the rapid development of the TFT-LCD is more based on an amorphous silicon platform (certainly, a small part of the products also use polycrystalline silicon), which has cheap price, simple technology and better uniformity; so, there are 55 inches, 65 inches and other larger size of products at present; the larger the size is, the higher the impedance of the line is; the metal wirings which are more coarse and thicker, and have better electric conductivity are required; the thickness cannot be increased infinitely, the materials with best electric conductivity are metal silver and copper, the better practical conductive materials may not be expected to have a breakthrough within a long time, only the width of the line can be increased, thus further reducing the aperture ratio of the TFT-LCD.
3) narrower acceptable environment temperature, mainly because the liquid crystal state only can exist in a very narrow temperature range; generally, the liquid crystal phase material used for the TFT-LCD only can exist under −20-70 degrees centigrade; in some special occasions, the liquid crystal materials under −30-100 degrees centigrade also can be used, but this is basically close to the limit; in some special occasions, such as the South and North poles, the aerospace and the higher-temperature environments, the liquid crystal is not quite good.
4) low response speed; as the TFT-LCD cannot automatically give out light, but to control the penetration and blockage of the light by taking the liquid crystal as the light valve, the response speed of the liquid crystal is very important; however, as the liquid crystal itself has higher viscosity, especially the negative liquid crystal used for vertical alignment, the response speed only can achieve the millisecond level, and is not a match on the microsecond speed of the OLED.
5) larger frame: because of using the alignment film and liquid crystal, the frame needs to be sealed by the frame material, and also needs backlight; the frame of the TFT-LCD cannot be smaller, and the minimum frame capable of being mass produced is approximately 4 mm.
At present, most of the frame materials of the LCD are the mixture of poly-epoxy resin, cellulose, diatomite, ultraviolet initiator and ultraviolet terminating agent, wherein the poly-epoxy resin, the ultraviolet initiator and the like may pollute the liquid crystal. As the oxygen of the epoxy resin has P orbital electron pairs and smaller steric hindrance, it may form the coordination compound with the benzene ring in the liquid crystal molecules, thus changing the state of the liquid crystal phase, causing uneven display brightness, and causing the phenomenon of various traces. In order to reduce the traces, the frame material is expected to achieve a certain polymerization degree before contacting the liquid crystal in the display area; and in order to achieve this purpose, a certain distance between the liquid crystal and the frame material must be guaranteed, and even so, there is some pollution in the near areas.
The disadvantages are almost the advantages of the OLED, but the TFT-LCD has more mature production technology, more mature and stable supply chains, and more competitive cost advantages than the PLED; therefore, the TFT-LCD is also the main stream of the display technology for a long time in the future; aiming at the above disadvantages, a certain discussion and improvement on the material technology are expected; the new high-molecular liquid crystal material is adopted as the frame material; as the high-molecular liquid crystal material itself is a liquid crystal, it can reduce the pollution to the small-molecular liquid crystal in the panel, thus achieving the purpose of reducing the frame of the LCD.